1. Field of the Invention
The present invention relates generally to lithographic printing presses and more particularly it concerns a device for disengaging the drive gearing of a seal-type dampener from the drive train of an offset lithographic printing press.
2. Description of the Prior Art
In the sheet-fed printing industry there are two basic classes of dampeners in use today. They are ductor-type dampeners and continuous-type dampeners.
Ductor-type dampener systems, although still sometimes sold by press manufacturers, are all but obsolete. This is because of the systems' inability to provide an even supply of dampening solution to the printing plate, thereby leading to poor ink-water balance.
Continuous-type dampener systems, in contrast, have become the preferred method of plate dampening because of their superior ability to evenly feed fountain solution to the plate, and thereby provide much improved ink-water balance. Continuous-type systems can be broken down into two species. They are the pan-fed-type continuous dampener systems (hereinafter described as pan-type dampeners) and the nip-fed/seal-type continuous dampener systems (hereinafter described as seal-type dampeners).
Of the pan-type dampeners there are essentially three sub-species: non-integrated, fully integrated, and partially integrated. The difference between these three sub-species depends on whether the pan-type dampener is tied only to the press's plate cylinder, tied only to the press's first ink form roller, or tied to both the press's plate cylinder and first ink form roller, respectively. All three types function essentially the same, though, can vary in complexity depending on the mechanism used to operate the configuration. Examples of pan-type dampener systems are seen in the prior art dampening systems of Dahlgren, U.S. Pat. No. 3,168,037, and MacConnell et al., U.S. Pat. No. 5,158,017. Characteristics common to the pan-type dampener species are a pan roller dipping into a fountain solution pan; a variable speed motor for driving the pan roller at speeds less than that of the plate cylinder; a metering roller in contact with the pan roller; at least one rubber coated form roller in contact with the printing plate and/or a bridging roller in contact with the first ink form roller, depending on whether the dampener is integrated or not; and one to several transfer rollers between the form and/or the bridging roller and metering roller to mill and transfer the fountain solution.
There are few variations between seal-type dampeners. Several examples of seal-type dampeners are seen in the prior art dampening systems of Fugman et al., U.S. Pat. No. 3,769,909, and Laudon, U.S. Pat. No. 4,455,938. Characteristics common to the seal-type dampeners are a hard metering roller, a rubber form roller in contact with the hard metering roller and in contact with the printing plate, seals enclosing the ends of the V-shaped nip formed between the metering and form rollers, a fountain solution feed system feeding solution to the V-shaped nip, and a press driven dampener drive gear attached to and driving either the form roller or metering roller. A variation of the typical seal-type dampener can be seen in the prior art dampening system of Hayes et al., U.S. Pat. No. 5,134,935. In this invention the dampener is similar to that of the Fugman et al. and Laudon patents excepting the fountain solution is pulled from a pan by the metering roller.
Until recently, the majority of large sheetfed press manufacturers offered either a ductor-type system of their own design, a pan-type continuous dampener system of their own design, or a pan-type continuous dampener system designed by a third-party vendor. Most customers choose to purchase one of the pan-type dampener designs over the ductor-type system. Nowadays, however, more and more manufacturers are offering, and customers are purchasing, the seal-type dampener system because they are beginning to recognize the benefits that the system has over the pan-fed dampener design. The benefits become apparent when the two systems are compared side-by-side.
The pan-type continuous dampener system requires at least three, but more often has four or five, rollers in the roller train. Each of these rollers must be cleaned between color changes and at the end of the workday, periodically adjusted to each other and maintained, and, when worn out or damaged, replaced. Since the seal-type dampener requires only two rollers to operate properly, roller cleaning, periodic adjustment and maintenance, and replacement is relatively much easier to carry out and much less costly.
In addition, pan-fed dampener systems use a motor and complex controlling electronics to drive the pan roller. The initial cost and maintenance of this equipment is extremely high. Because the seal-type dampening system does not require a motor, but is instead gear driven by the press gear train, the additional costs do not exist.
And, in spite of the more apparently sophisticated design of the pan-fed systems, they require a skilled operator to rim. In contrast, the seal-type system requires little operator attention during printing leaving more time to deal with other aspects of the printing operation.
Finally, because pan-fed systems usually require a percentage of alcohol in the fountain solution to ensure optimum fluid control, a fountain solution recirculator system is usually a necessary attachment to chill and maintain the alcohol concentration. These recirculators add considerable cost to the purchase and maintenance of the dampener systems. The seal-type system, on the other hand, does not require alcohol, therefore a recirculator system is unnecessary.
In sum, the pan-fed dampener system, when compared to the seal-type dampening system, initially costs more to purchase, requires a more skillful press operator to run, takes more effort to maintain, and costs more to repair.
But, seal-type systems have one notable disadvantage when compared to pan-fed systems: the inherent inability to disengage the dampener unit from the press drive train when the dampener is not needed for printing. This fact only became apparent recently because it was only until a short while ago that seal-type dampener systems started to be used on multi-head presses. Previously, the systems were found only on single-head duplicators (generally defined as presses having only one printing head and a plate width approximately less than or equal to 18 inches). Now, because of its emerging popularity on medium to larger sheet size multi-head presses, this limitation has come to light.
There are several reasons printers will not use one or several heads of their multi-head press. The most obvious is that the job being run requires less colors than the number of color heads on the press.
Unlike the seal-type system, the pan-fed system can be easily turned off by deenergizing the pan-roller motor and withdrawing the typically friction driven form roller from the press's plate cylinder and/or, if partially or fully integrated, the bridging roller from the press's first ink form roller.
Because seal-type systems are directly driven by the press's gear train, the press operator cannot turn the system off and has the option of either leaving the seals in and allowing the unit rollers and seals to run dry during printing, thereby causing premature wear of the rollers and seals; removing the seals and allowing the unit rollers to run dry during printing, thereby subjecting the rollers to premature wear; or leaving the seals in and filling the nip with water during printing, thereby reducing, though not eliminating, wear on the rollers and seals. All three options required extra effort by the operator and even the least harmful to the unit, adding water to the nip, does not completely eliminate unwanted wear and tear to the dampener. Said wear inevitably requires the press owner to pay higher maintenance costs in the form of early seal and roller replacement.